newlib/config/tls.m4

dnl Check whether the target supports TLS.
AC_DEFUN([GCC_CHECK_TLS], [
  AC_REQUIRE([AC_CANONICAL_HOST])
  GCC_ENABLE(tls, yes, [], [Use thread-local storage])
  AC_CACHE_CHECK([whether the target supports thread-local storage],
		 gcc_cv_have_tls, [
    AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
      [dnl If the test case passed with dynamic linking, try again with
       dnl static linking, but only if static linking is supported (not
       dnl on Solaris 10).  This fails with some older Red Hat releases.
      chktls_save_LDFLAGS="$LDFLAGS"
      LDFLAGS="-static $LDFLAGS"
      AC_LINK_IFELSE([int main() { return 0; }],
	[AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],
		       [gcc_cv_have_tls=yes], [gcc_cv_have_tls=no],[])],
	[gcc_cv_have_tls=yes])
      LDFLAGS="$chktls_save_LDFLAGS"
      if test $gcc_cv_have_tls = yes; then
	dnl So far, the binutils and the compiler support TLS.
	dnl Also check whether the libc supports TLS, i.e. whether a variable
	dnl with __thread linkage has a different address in different threads.
	dnl First, find the thread_CFLAGS necessary for linking a program that
	dnl calls pthread_create.
	chktls_save_CFLAGS="$CFLAGS"
	thread_CFLAGS=failed
	for flag in '' '-pthread' '-lpthread'; do
	  CFLAGS="$flag $chktls_save_CFLAGS"
	  AC_LINK_IFELSE(
	    [AC_LANG_PROGRAM(
	       [#include <pthread.h>
		void *g(void *d) { return NULL; }],
	       [pthread_t t; pthread_create(&t,NULL,g,NULL);])],
	    [thread_CFLAGS="$flag"])
	  if test "X$thread_CFLAGS" != Xfailed; then
	    break
	  fi
	done
	CFLAGS="$chktls_save_CFLAGS"
	if test "X$thread_CFLAGS" != Xfailed; then
	  CFLAGS="$thread_CFLAGS $chktls_save_CFLAGS"
 	  dnl Test for an old glibc bug that violated the __thread property.
	  dnl Use volatile to ensure the compiler won't optimize away pointer
	  dnl accesses it might otherwise assume to be redundant, or reorder 
	  dnl them and reuse storage, which might lead to them pointing to
	  dnl the same location.
	  AC_RUN_IFELSE(
	    [AC_LANG_PROGRAM(
	       [#include <pthread.h>
		__thread int a;
		static int *volatile a_in_other_thread;
		static void *
		thread_func (void *arg)
		{
		  a_in_other_thread = &a;
		  return (void *)0;
		}],
	       [pthread_t thread;
		void *thread_retval;
		int *volatile a_in_main_thread;
		a_in_main_thread = &a;
		if (pthread_create (&thread, (pthread_attr_t *)0,
				    thread_func, (void *)0))
		  return 0;
		if (pthread_join (thread, &thread_retval))
		  return 0;
		return (a_in_other_thread == a_in_main_thread);])],
	     [gcc_cv_have_tls=yes], [gcc_cv_have_tls=no], [])
	  CFLAGS="$chktls_save_CFLAGS"
	fi
      fi],
      [gcc_cv_have_tls=no],
      [dnl This is the cross-compiling case. Assume libc supports TLS if the
       dnl binutils and the compiler do.
       AC_LINK_IFELSE([__thread int a; int b; int main() { return a = b; }],
	 [chktls_save_LDFLAGS="$LDFLAGS"
	  dnl Shared library options may depend on the host; this check
	  dnl is only known to be needed for GNU/Linux.
	  case $host in
	    *-*-linux*)
	      LDFLAGS="-shared -Wl,--no-undefined $LDFLAGS"
	      ;;
	  esac
	  chktls_save_CFLAGS="$CFLAGS"
	  CFLAGS="-fPIC $CFLAGS"
	  dnl If -shared works, test if TLS works in a shared library.
	  AC_LINK_IFELSE([int f() { return 0; }],
	    [AC_LINK_IFELSE([__thread int a; int b; int f() { return a = b; }],
	      [gcc_cv_have_tls=yes],
	      [gcc_cv_have_tls=no])],
	    [gcc_cv_have_tls=yes])
	  CFLAGS="$chktls_save_CFLAGS"
	  LDFLAGS="$chktls_save_LDFLAGS"], [gcc_cv_have_tls=no])
      ]
    )])
  if test "$enable_tls $gcc_cv_have_tls" = "yes yes"; then
    AC_DEFINE(HAVE_TLS, 1,
	      [Define to 1 if the target supports thread-local storage.])
  fi])

dnl Check whether the target assembler supports TLS.
AC_DEFUN([GCC_CHECK_CC_TLS], [
  GCC_ENABLE(tls, yes, [], [Use thread-local storage])
  AC_CACHE_CHECK([whether the target assembler supports thread-local storage],
		 gcc_cv_have_cc_tls, [
    AC_COMPILE_IFELSE([__thread int a; int b; int main() { return a = b; }],
      [gcc_cv_have_cc_tls=yes], [gcc_cv_have_cc_tls=no])]
    )])
  if test "$enable_tls $gcc_cv_have_cc_tls" = "yes yes"; then
    AC_DEFINE(HAVE_CC_TLS, 1,
	      [Define to 1 if the target assembler supports thread-local storage.])
  fi])

dnl Check whether TLS is emulated.
AC_DEFUN([GCC_CHECK_EMUTLS], [
  AC_CACHE_CHECK([whether the thread-local storage support is from emutls],
  		 gcc_cv_use_emutls, [
    gcc_cv_use_emutls=no
    echo '__thread int a; int b; int main() { return a = b; }' > conftest.c
    if AC_TRY_COMMAND(${CC-cc} -Werror -S -o conftest.s conftest.c 1>&AS_MESSAGE_LOG_FD); then
      if grep __emutls_get_address conftest.s > /dev/null; then
	gcc_cv_use_emutls=yes
      fi
    fi
    rm -f conftest.*
    ])
  if test "$gcc_cv_use_emutls" = "yes" ; then
    AC_DEFINE(USE_EMUTLS, 1,
      	      [Define to 1 if the target use emutls for thread-local storage.])
  fi])